"Kanada, Mexico and USA."

Firstly, Canada starts with a C, not a K, unless you are basing the name of the country given to it by the St. Lawrence Iroquoians, of which it would be "Kanata", not Kanada.

Kanada is a Hindu sage who founded the philosophy of Vaisheshika.

"automatically the marketplace was assigned"

You signed up on Amazon.com. That gives you a North American Unified Account, which is based in the USA, and lets you sell in Canada and Mexico at no additional charge.

"I would like to change this in order to be assign to Germany. How to do this?"

You would have had to sign up to be a seller on Amazon.de as that is the Germany marketplace. https://sell.amazon.de/